Fertilized Japanese quail eggs were exposed during the first 12 days of embryonic development to 2.45 GHz microwaves of an incident power density of 5 mW/square cm (SAR equals 4.03 W/kg). The quails were allowed to mature and were mated over a 16-week period. Fertility was significantly reduced using matings of exposed males with both exposed and control females while hatchability of fertile eggs was unchanged. Spermatozoal numbers and motility in semen samples which were collected manually were significantly reduced (P is less than 0.01) in the exposed males. Other eggs exposed as described above were reared to 22 weeks of age. Circulating numbers of leucocytes, reticulo endothelial function, and primary humoral immunity were evaluated. Leucocytes were elevated significantly in exposed quail (10.17 times 10 to the 3rd power versus 8.29 times 10 to the 3rd power cells/cubic mm). No other indices were significantly different.